COLLECTION CHOICE : Material that is worth working with needs to have fruitbodies that show the True Color of the species. Young buttons are very desirable too, but not always available. There is absolutely no point to collect old, browned-out fruitbodies.
GOOD PHOTO: Please show all relevant details -- see examples of some Cortinarius Group Portraits. Collections without a good photo serve no useful purpose.
a) Cap and Surface Detail -- it is important to see if there are veil patches, and appreciate the type of pileal covering.
b) Gills -- check the attachment (typically sinuate) and also whether the edges are even.
c) Context -- the coloration and potential discoloration of the context are critical diagnostic characters. 
d) Veil color -- veil color is a critical diagnostic feature, but it is not always apparent when buttons are not available.  It can be judged by other means, l;ike remnants on the stipe, bulb, etc.
Some Examples of Group Portraits

HABITAT: Cortinarius are ectomycorrhizal fungi. Please make basic notes on the habitat in order to guesstimate the possible tree hosts. One doesn't need to do a botanic treatise, but just to note the type of the dominant tree flora.

Conifer -- some basic idea of the kind of conifers is important. There are huge differences between Douglas Fir, Coastal Pines, Montane Pines, True Firs, Spruce, Hemlock. This can be very critical diagnostic feature. In the Spruce parts of California we see different Corts than in the Live Oak Mediterranean part...
Broadleaved -- specify the basic trees -- Oak, Tanoak, Madrone, Manzanita, California Bay, etc.
Mixed -- still some basic idea is important -- is it a typical Inland Pine/Oak, or the Coastal Redwood/Doug Fir/Tanoak. A note on the presence/absence of Tanoak is very important

Most Corts are void of interesting odors, but some have very diagnostic such. Cortinarius albofragrans (commonly under Live Oak) has a very fragrant odor.

Taste: Too much to ask for most people, but in some cases this is very diagnostic -- Cortinarius infractus can be ascertained that way

Bruising Reactions: Note any interesting discoloration as a results of handling and injury. There are several species that are uniquely identified by their bruising reaction.

Cortinarius traganus -- the combination of odor, context and overall color define this species in the field quite easily
MACROCHEMICAL TESTS Various macrochemical reactions are recorded for Cortinarius, but the color effects of KOH are critically important. This is particularly for the fleshy members of Subgenus Phlegmacium.  The coloration falls into 4 main groups: None, Brown, Yellow or Pink/Red. Making a note of these, or pictures (far preferred) can immediately places the collection in the right Section and minimize a lot of cold Id effort. Please apply the KOH to the following surfaces:(1) Pileus (2) Context (3) Bulb (if present), (4) Mycelial strands (if present).

It is always a good idea to put a drop of water (as a negative test) and compare against the KOH

Brownish reaction suggest Sections Caerulescentes or Glaucopodes for this Blue Cort.

Pinkish/Reddish reaction strongly suggests Section Calochroi for this Blue Cort. This eliminates a number of possibilities and narrows down our search to C. sodagnitus.

Distinct yellow reaction. Quite common for some Sections, particularly Variecolores

Application to the mycelial strands of Cortinarius calochrous.